The current thermal barrier coatings (TBCs) may reach their application limits in high advanced gas turbines due to the limited capacities to control their micro-structure from the process parameters and the reduced choice of materials suitable for thermal plasma spraying. One way to overcome these limitations is to move away from the TBC coatings and replace them with so called ceramic tiles which can be fixed on the surface of the heat exposed component with different fastening technologies.
In the document U.S. Pat. No. 4,563,128 ceramic tiles are clamped in dovetail type recesses in the flank area of a turbine blade.
The document EP 0 895 028 B1 discloses a ceramic lining for combustions spaces comprising at least one wall panel, made of a heat resistant structural ceramic. Said wall panel provides an opening through which a fastening element being arranged for fastening said wall panel to the inner wall of the combustor.
The document U.S. Pat. No. 7,198,860 B2 discloses a ceramic tile insulation for gas turbine components with a multitude of ceramic tiles which are bonded to a heat exposed surface of a gas turbine component. A first layer of individual ceramic tiles are bonded to the surface of the gas turbine component which is of ceramic material. A second layer of individual tiles is bonded on top of the first layer.
EP 1 772 441 A1 is generally related to high purity zirconia-based and/or hafnia-based materials and coatings for high temperature cycling applications. Thermal barrier coatings made from the invention high purity material was found to have significantly improved sintering resistance relative to coatings made from current materials of lower purity. The invention materials are high purity zirconia and/or hafnia partially or fully stabilized by one or any combinations of the following stabilizers: yttria, ytterbia, scandia, lanthanide oxide and actinide oxide.
The production of ceramic tiles allows a strict layered control of the microstructure on various levels in respect to grain size, pore size, porosity, pore shape and pore distribution. However, solid ceramics, equally to TBC, have a pure thermal shock and thermal gradient resistance. Therefore the current TBCs are strongly micro-cracked in addition to their high “macro-porosity” both being linked directly by the processing parameters. Micro-cracking occurs while the TBC-layer gets in contact to the cold surface of the component during the TBC-coating applied by plasma or electron beam physical vapor deposition-technique.
The constant and reproducible quality requirements for the production of ceramic tiles to be used as thermal protection in gas turbines imposes a fully controlled “defect”-free production method to limit any random effects affecting the ceramic performance. Such controlled processing methods usually result in a micro-crack-free ceramic structure. The high elastic modulus resulting from such a structure and the high thermal-mechanical formation itself may not be critical but the accompanied acoustic shock wave causes a catastrophic disintegration of the ceramic.